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The Official Edexcel CH5 Revision Thread! (22/06/05 AM) watch

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    Can we discuss unit 5 here for preparation for the Monsta that is UNIT 5 CHEM....HAS ANY1 SEEN ANY DODGY THINGS IN PAPERS...CUD THEY NOTE THEM ASWELL... :tsr:
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    22nd or 23rd? :confused:
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    o 23rd DARN
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    Had me worried there for a bit!
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    (Original post by kpg)
    Had me worried there for a bit!
    soz

    how u findin unit 5??..hav u dun ne papers..
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    i did ma first 1 2day june 2004..have u dun it?
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    I think so, can't remember the dates but I've done about 4 or 5 past papers. Think I'm pretty clued up anyway.
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    can someone please explain part b in spec for 5.1
    about procedures and principles to estimate reducing agents and oxidisiing agents.
    the NAS book explain it so bad, does anyone have a method for these tirations.

    thanks
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    To find the conc of Oxidising agents :

    -Add a known amount of oxidising agent to excess acidified potassium iodide
    -This will give off (liberate) iodine which is titrated against a standard solution of sodium thiosulphate
    -When the iodine starts to become a pale straw colour, starch is added as an indicator
    -Solution is now blue/black and more thiosulphate is added until this disappears.

    Equation you need to know is :

    I2 + 2Na2S2O3 ---> 2NaI + Na2S406

    To find the conc of Reducing agents :

    -Add a known amount of reducing agent to conical flask
    -Add known amount of sulphuric acid
    -Add standard potassium manganate (VII) to burette and run it into the conical flask
    -End point is when a pale pink colour is obtained (this is Mn2+)
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    thanks a lot!!!
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    this is ma nxt xam...how is every1 findin revisin 4 it...i g2 CANE this for ne chance of an A
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    CH5 is hard I think. I keep getting the apparatus questions horribly (and dangerously) wrong for the prodecures, and have to put in a lot of effort to remeber the mechanisms and stuff. ch4 is much nicer to work with I think..
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    Check out www.chemguide.co.uk - its absolutely brilliant and has helped me no end with revision. I don't think unit 5 is that hard- there isn't too much to learn that we haven't learnt before.
    The mechanisms questions are pretty similar....get 'make the grade'-thats great!
    Just look at the question, and imagine the mark scheme-its worked for me so far
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    --------------------------------------------------------------------------------

    Okay, Im doing my exam for Unit 5 this week, and Im so screwed, I need to advice on how to pass the exam resonably, you see I started falling behind in chemistry last year but my other subjects where fine, I fell so far behind that when I was in A2 I was just getting slaughtered, anyway I only need a D cuz my other subs are gonna cover the rest of my points. Basically I havnt really started revising, I got an E on Unit 4 and the teacher was surprised haha, he recommanded that I dont bother resitting and I push all my efforts into Unit 5 and Syp, he said this because I told him I am aiming for a D, plus my AS grade is a mid C, as it stands now, I am on a mid D.

    Can any1 give me some advice on pulling to average D's off, btw I am really behind in Chemistry, I hate it, I cant do it, because I didnt pay attention to the basics, and Im so lost, i just kinda of blanked it out of my mind, anyway I need 50% on unit 5, any help would be appreciated, or advice

    I am terrible at organic, and any kind of reactions, my maths skills are fine, and Im fine at learning hard facts, just cant do the chemistry.

    ANY HELP PLEASE!!!!!!!
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    (Original post by reaper93)
    --------------------------------------------------------------------------------

    Okay, Im doing my exam for Unit 5 this week, and Im so screwed, I need to advice on how to pass the exam resonably, you see I started falling behind in chemistry last year but my other subjects where fine, I fell so far behind that when I was in A2 I was just getting slaughtered, anyway I only need a D cuz my other subs are gonna cover the rest of my points. Basically I havnt really started revising, I got an E on Unit 4 and the teacher was surprised haha, he recommanded that I dont bother resitting and I push all my efforts into Unit 5 and Syp, he said this because I told him I am aiming for a D, plus my AS grade is a mid C, as it stands now, I am on a mid D.

    Can any1 give me some advice on pulling to average D's off, btw I am really behind in Chemistry, I hate it, I cant do it, because I didnt pay attention to the basics, and Im so lost, i just kinda of blanked it out of my mind, anyway I need 50% on unit 5, any help would be appreciated, or advice

    I am terrible at organic, and any kind of reactions, my maths skills are fine, and Im fine at learning hard facts, just cant do the chemistry.

    ANY HELP PLEASE!!!!!!!
    aww... I need 50% aswell!

    Spend all your time on organic chemistry...really! You can score ALOT of marks by just memorizing the organic (esp for the synoptic as one question is bound to be organic and one on calculations...so you will be sorted if you ace those 2/3 questions ).
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    wat raw mark out of 75 do u need on average to get 90/90...AIM HI ACHIEVE LO...AIM LO ACHIECE NTTIN lol
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    err.. 75 to be garunteed it, anything else and it depends on the difficulty of the exam, which nobody knows at the moment
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    sfteee....cud sum1 answa this q plz....
    Explain in terms of structure and bonding why benzene and propene react differently with electrophiles. (4)
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    Cud sum1 show me how the 6 aqua ligand join the Cr3+ ion...orbital styleeeee
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    (Original post by mackin boi)
    sfteee....cud sum1 answa this q plz....
    Explain in terms of structure and bonding why benzene and propene react differently with electrophiles. (4)
    -Benzene has a delocalised system of pi electrons, above and below a flat/planar benzene molecule. This stabilises the benzene molecule comparitivley
    -Electrophiles attracted to the delocalised pi electrons
    -When an electrophile reacts it forms a covalent bond with benezene on a carbon and the hydrogen is there too, this however disturbs the delocalised ring
    -Subst. happens rather than addition because it's energetically favourable for the hydrogen to be lost (pair of electrons back into the ring) and the delocalisation to be restored
    -Propene has a double bond : a sigma bond because of the overlap of s orbitals and a pi bond above and below the two carbons because of an overlap of p orbitals
    -When propene reacts the double bond breaks and two sigma bonds are formed which is energetically favourable

    Not explained very well but that's the general idea.
 
 
 
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